The present invention relates to a solid state imaging device and a method for manufacturing a solid state imaging device.
CCD image sensors are widely used as imaging devices for digital cameras and other types of equipment. For example, a frame transfer CCD image sensor is a known type of CCD image sensor.
Referring to FIG. 1, a frame transfer CCD image sensor includes an imaging section 100P for performing photoelectric conversion, a storage section 100C for temporarily storing the photoelectric-converted charges, and a horizontal transfer section 100H for supplying the charges stored in the storage section 100C to an output section 1005.
The imaging section 100P performs photoelectric conversion in correspondence with an irradiated optical image for each pixel. Information charges that are photoelectric-converted in the imaging section 100P are transferred at a high speed (frame shifted) in frame units to the storage section 100C. The information charges for one frame stored in the storage section 100C are transferred to the horizontal transfer section 100H one line at a time. The information charges stored in the horizontal transfer section 100H are sequentially transferred to the output section 100S one pixel at a time. The information charges transferred to the output section 100S are converted to a voltage value to generate an image signal of the CCD image sensor that is provided to a signal processor (not shown).
Such transfer of information charges is performed by applying voltages to each gate electrode (transfer electrode) of the CCD image sensor. More specifically, transfer clocks (drive voltages) of, for example, three different phases (ΦP1 to ΦP3, ΦC1 to ΦC3) are applied to predetermined gate electrodes of the imaging section 100P and the storage section 100C to transfer information charges. Transfer clocks (drive voltages) of, for example, two different phases (ΦH1, ΦH2) are applied to predetermined gate electrodes of the horizontal transfer section 100H to transfer information charges.
FIG. 2 is a plan view showing an imaging section in a CCD image sensor. As shown in FIG. 2, a plurality of gate electrodes 121 corresponding to pixels for the three primary colors of red (R), green, (G), and blue (B) are arranged on a silicon substrate 110 with a gate insulation film (not shown) applied between the silicon substrate 110 and the gate electrodes 121. An interlayer insulation film is formed on the gate electrodes 121. A plurality of clock wires 140, extending in the direction information charges are transferred from the imaging section 100P (FIG. 1) to the storage section 100C (FIG. 1), are formed on the interlayer insulation film. Each clock wire 140 is electrically connected to associated gate electrodes 121 by connection holes 141, which are arranged in the transfer direction and formed in every third gate electrode 121. The transfer clocks ΦP1 to ΦP3 of three difference phases are applied to the clock wires 140 so that the same voltage is applied to every third gate electrode 121 on each clock wire 140.
FIG. 3 is a schematic cross-sectional view showing the imaging section in the CCD image sensor. As shown in FIG. 3, in the CCD image sensor, p-type impurities are injected into a predetermined region of an n-type silicon substrate 110 to form a p-well 111. Further, n-type impurities are injected into predetermined regions of the p-well 111 to form a plurality of channel regions 112 associated with pixels for red (R) (not shown), green (G), and blue (B). The gate electrodes 121 are formed on a gate insulation film 120 above the silicon substrate 110.
The channel regions 112 associated with the pixels cooperate with the p-well 111 to form light receiving pixels, which receive light and perform photoelectric conversion. The information charges stored in the light receiving pixels are transferred to the storage section 100C (FIG. 1) by applying voltages to the gate electrodes 121 from the clock wires 140 via the connection holes 141 (FIG. 2).
An interlayer insulation film 122, which covers the gate electrodes 121, is formed on the silicon substrate 110. A color filter 124 for red (R) (not shown), green (G), and blue (B), which are designated in a regular manner in correspondence with the pixels, is formed on the interlayer insulation film 122. A planarizing film 125, which is, for example, acrylic, is formed on the color filter 124.
A microlens (not shown) converges the incident light of the CCD image sensor at a central portion of each channel region 112, which forms a light receiving pixel. Photoelectric conversion is performed at the central portion. Before the incident light reaches the channel regions 112, the color filter 124 first selectively transmits light corresponding to predetermined primary colors and cuts out other light. Thus, in each channel region 112, photoelectric conversion is performed in correspondence with the light of the primary color selectively transmitted in association with the color filter 124.
In such a CCD image sensor, diagonal incident light transmitted through an adjacent portion of the filter 124 may be received by a light receiving pixel that differs from the intended light receiving pixel. More specifically, referring to FIG. 3, diagonal light L1 entering, for example, a blue (B) portion of the filter 124 may be received by a light receiving pixel that corresponds to green (G). In such a case, the light receiving pixel corresponding to blue (B) should photoelectric-convert a signal. However, the light receiving pixel corresponding to green (G) adds a green component to a blue component. This mixes colors and affects the color reproduction characteristic in an undesirable manner.
In recent years, there is a tendency for the number of pixels to be increased to improve resolution in a solid state imaging device. At the same time, there is a demand for a more compact solid state imaging device. Thus, pixels are being miniaturized and laid out with higher integration. As a result, the mixing of colors due to diagonal light has become more problematic.
In addition to a frame transfer CCD image sensor, diagonal light also affects color reproduction in an undesirable manner as described above in a solid state imaging device provided with a color filter.
Further, in addition to a solid state imaging device provided with color filters, when diagonal light enters an adjacent pixel, the reproduction characteristic of an optical image is affected in an undesirable manner in a so-called monochrome CCD image sensor.